How to avoid float texture limit for GPU rendering
It looks like what you've found is accurate.  Here is an excerpt from the manual http://www.blender.org/manual/render/cycles/gpu_rendering.html so far as I know it's current for mid-2015


  Limitations
  
  The maximum amount of individual textures is limited to 95 byte-image
  textures (PNG, JPEG, ..) and 5 float-image textures (OpenEXR, 16 bit
  TIFF, ..) on GTX 4xx/5xx cards, and 145 byte-image textures and 5
  float-image textures on GTX6xx cards and above.